1. Field of the Invention
The present invention is directed to forming composite parts and, more particularly, to a vacuum assisted resin transfer molding method and apparatus for forming composite parts by infusing different sections of the part to be formed separately and then joining the sections by an additional infusion process.
2. Description of the Related Art
Known methods and apparatus have been used to impregnate dry fibrous materials by introducing a resin to the material under vacuum conditions, and then curing the resin to produce the composite part. One particular method employing a vacuum bag molding process, or vacuum assisted resin transfer molding (VARTM) process, includes placing a fiber lay-up in a rigid mold having a shape corresponding to the composite part being produced. Notably, such processes take advantage of a desired amount of compression provided by a vacuum bag used to enclose the resin impregnated fiber lay-up under vacuum pressure. To promote uniform and complete xe2x80x9cwet-outxe2x80x9d of the fiber lay-up, the vacuum operates to remove entrapped air in the lay-up as its formed into the composite structure. As a result, such systems generally avoid the creation of areas of the lay-up that are not infused with resin, which can compromise the structural integrity of the part. After wetting-out the fiber, the resin is then cured to complete the structure.
The lay-ups used in known systems for manufacturing solid and cored laminate composite structural members are typically made from glass or carbon fiber or polyester cloth. To enhance structural characteristics of the member, such systems typically employ a number of plies of such fiber-reinforced material. Notably, known vacuum assisted resin transfer molding processes have been used to manufacture non-cored structures, as well as cored structures that include a core material disposed in the lay-up.
With more particular reference to making non-cored structures, a fibrous lay-up is initially placed in a self-contained mold having a desired shape. Then, typically, a resin distribution medium is placed on top of the lay-up. The medium separates the lay-up from a structure for maintaining vacuum pressure in the system, such as a flexible vacuum bag, and facilitates flow of uncured resin in the system by providing flow paths between the bag and the lay-up. The vacuum bag is fluid impervious and sealed to allow applied vacuum pressure to pull the resin through the fibrous lay-up, as noted previously. Also, a resin inlet is disposed, preferably, adjacent to the vacuum bag with the bag being sealed thereto to maintain vacuum pressure.
Similar apparatus is used to manufacture cored structures. However, the fibrous lay-up employed in manufacturing cored structures includes, typically, fiber-wrapped core structures made of, for example, balsa wood. As with the non-cored structures, the lay-up is then placed in a rigid mold and a vacuum bag is placed thereon to maintain vacuum pressure. Further, a distribution medium may be employed, either between the core structures and the fibrous material wrapped thereon, or between the fiber wrapped cores and the vacuum bag, to promote uniform resin flow upon application of vacuum pressure. For both cored and non-cored structures, the resin is then cured and the composite part and the rigid mold are separated.
One challenge presented by such processes is that during manufacturing, the weight of the structure typically becomes extreme, and the fibrous lay-up including the layers of fiber-reinforced material exhibits poor resin flow characteristics. Improvements in known apparatus and methods for impregnating fiber-reinforced resin have included using a fibrous lay-up comprising a filament winding that orients the fibers to facilitate more efficient resin flow. Moreover, to further facilitate uniform wet-out, a distribution medium may also be employed to distribute the resin during impregnation. However, known vacuum assisted resin transfer molding methods still have inherent drawbacks.
One disadvantage of known vacuum assisted resin transfer molding processes, whether used for forming cored or non-cored structure, is that large structures and structures having unconventional shapes are difficult to manipulate and extract from the self-contained molds employed. For example, in one application of particular interest, a number of problems arise when making hollow tubular composite structures using vacuum assisted resin transfer molding processes. In one known VARTM method, an inflatable bladder is employed as a temporary mold core. Further, dry fiber-reinforced fabric is disposed around the bladder intermediate the bladder and an outer rigid tubular mold. In this case, the bladder is inflated to press the fibrous pre-form against the outer mold during resin infusion.
After curing the resin as described above, the bladder must be removed. Unfortunately, for large structures, there is a large volume of air contained by the bladder, especially in view of the fact that the pressure must be maintained at a significant level to support the dead weight of the fibrous pre-form and the associated resin. In the event that the bladder bursts, the outcome can be a significant change in air pressure in the building in which the composite part is being manufactured. This instantaneous change in air pressure can be extremely dangerous. As a result, such known systems have been capable of producing only relatively small diameter tubes. Because it would be desirable to make composite tubes having, for example, a six foot diameter, a new technique was required.
Similar problems are encountered when attempting to produce complex shapes, especially large complex shapes. The tooling for such structures becomes prohibitively expensive, and the resulting composite structures are difficult to remove from the tooling. Moreover, in some cases, the large structures cannot be removed from the mold at all. In that case, the mold typically must be broken away or otherwise separated from the completed composite part, thus compromising repeatability and increasing expense.
In view of the above drawbacks, the art of manufacturing resin-infused composite structures was in need of an improved method and apparatus for producing large structures, especially closed form structures and structures having odd shapes. The method and apparatus should ensure uniform resin wet-out of the fibrous pre-form, and maintain the overall integrity of the composite part being produced. Further, the tooling required for such a method and apparatus should also be cost effective and allow ready manipulation of the composite part being produced.
The preferred embodiment is directed to a method and apparatus of producing a composite part by separately infusing and curing different sections of a fibrous pre-form using a rigid mold having a shape corresponding to only a portion of the part to be formed. The method preferably includes forming two or more different sections of the composite part so that the sections include a non-resin-infused portion that can be subsequently and iteratively coupled, and then infused with resin to complete the part. As a result, tooling for the method and apparatus is minimized, and the integrity of the part being produced can be readily monitored. Notably, the method and apparatus of the preferred embodiment is particularly adapted to producing large composite parts and parts having unusual shapes.
According to a first aspect of the preferred embodiment, a method of making a composite part includes the steps of placing a first section of a fibrous pre-form in a mold and infusing the first section of the fibrous pre-form with a resin so as to produce a resin-infused portion and a non-resin-infused portion. Next, the method includes coupling the non-resin-infused portion to a second section of the fibrous pre-form to create a coupled non-resin-infused portion. Then, the coupled non-resin-infused portion is infused to create a second resin-infused portion and a second non-resin-infused portion.
In another aspect of the preferred embodiment, the method further includes translating the first section in the mold prior to the coupling step, and repeating the translating, coupling and second infusing steps until the composite part is complete.
According to another aspect of the preferred embodiment, the first and second sections of the fibrous pre-form each includes a plurality of layers of fiber-reinforced fabric, and wherein the coupling step includes stacking at least a portion of the layers of the non-resin-infused portion with at least a portion of the layers of the second section.
According to a still further aspect of the preferred embodiment, the fibrous pre-form includes a splicing section having a plurality of layers of fiber-reinforced fabric, and the coupling step includes stacking the layers of the splicing section with the layers of the first and second section.
In yet another aspect of the preferred embodiment, a method of making a composite part includes the steps of forming a first structure, the first structure including a fiber-reinforced material having a resin-infused portion and a non-resin-infused portion. The method also includes forming a second structure, the second structure including a fiber-reinforced material having a resin-infused portion and a non-resin-infused portion. Next, the method includes coupling the first and second non-resin-infused portions to create a coupled non-resin-infused portion. Then, the coupled non-resin-infused portion is infused with a resin and cured.
According to another aspect of the preferred embodiment, an assembly for forming a composite part includes a fibrous pre-form having first and second sections. The assembly also includes a rigid mold adapted to support said pre-form and having a shape corresponding to only a portion of the part, and a bleed channel positioned to wet out the first section with a resin so as to create a resin-infused portion and a non-resin-infused portion of the first section. In addition, the non-resin-infused portion is adapted to be stacked with a portion of the second section.
These and other objects, features, and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.